The overall goal of the proposed research is a richer understanding of the structural and physiological bases of frequency selectivity in the vertebrate auditory system. In particular, the primary objectives of the proposed research are to gain an understanding and appreciation of the mechanical and electrical factors underlying frequency resolution in the vertebrate auditory system, and to provide further insights into the mechanisms underlying stimulus interactions which affect tuning in the vertebrate inner ear. To accomplish the first objective, we intend to perform a series of three detailed investigations in order to (a) directly measure the motion of the tectorial membrane partition in response to sound and thus more precisely define the role of this structure in frequency analysis, (b) characterize in situ the temperature dependence of the tectorial membrane partition in its response to pure tones, and (c) systematically study the membrane properties of anatomically-defined hair cells from the amphibian papilla, and to relate these properties to the known tonotopic organization of the organ. To accomplish the second objective, we shall (d) extend our investigation of the interactions between acoustic and seismic stimuli on the recently characterized bimodal fibers in the eighth nerve, and (e) quantify the extent to which the extratympanic pathways to the inner ear play a role in sculpting the tuned responses of the peripheral auditory system. We believe that the data that result from this combined structure-function and neurethological approach will be rich in implications regarding the anatomical and neural substrate underlying the processing of complex sounds, and that this work will serve as a model for understanding fundamental problems of human speech perception in noisy environments.